Your derivative is not correct.
$f'(x) = -\dfrac{2}{(x-1)^2}$
Hence, your numerator was incorrect. Using the correct derivative, you should be able to get the correct answers (there will be more than one).
$-\dfrac{2}{(x-1)^2} = -\dfrac{1}{2}$
$(x-1)^2 = 4$
$x-1 = \pm 2$
$x = 1 \pm 2$, so either $x = -1$ or $x = 3$.
Then, $f(-1) = 0$ and $f(3) = 2$, so both lines should have slope $-\dfrac{1}{2}$, one should pass through the point $(-1,0)$ and the other through the point $(3,2)$.